O'Neal Slave owners in Tennessee

O'Neal Slave owners in Tennessee

I am a white decedent of who I believe is a Mulatto GGgrandfather who was born in 1850 in Nashville Tennessee. I have hit a brick wall in my research of him. The oldest record I can find of him is his marriage record to my GGgrandmother in 1894. My GGgrandfather was 43 years old when he married my white, 14 yr old GGgrandmother. I don't understand how my GGgrandfather lived for 43 years before he married her and I am not able to locate anything on the first 43 years of his life. All census records 1900 and later that I find him in list him as White, but photos of him and the lack of records lead me to believe he was of mixed race and may have been born into slavery and carried his slave owners last name.His name is Elijah O'Neal born 1850 in Nashville Tennessee. Thank you for any advice on how to find those missing years. Kboeds